do you have a nib with or without reservoir? It works better with reservoir so I put them on all the nibs. You do have to keep it dipped in the ink for a few seconds for the reservoir to fill up, which is something that’s not necessarily intuitive.

I've had good luck with cleaning the nib gently with an extra-soft fine toothbrush and a little toothpaste. Wash the natural oils off your fingers before handling the nibs as well.
As to the ink- some of my fountain pen inks absolutely refuse to work with my various dip pen nibs, while other ftn pen inks of mine work fine and coat/cling nicely.
Adding about 1/5 volume of Gum Arabic does work to adapt a small vial of ftn pen ink for dip pens, but then don't use that ink for your ftn pens. The gum-treated inks tend to dry a bit shiny and make shimmer inks less shimmery... something to keep in mind. There are dip pen-specific inks for sale, of course.
For black waterproof ink that works really well right out of the bottle in both ftn pens and dip pens, I like my De Atramentis 'Archive' black ink. It's luxurious! That ink can also be used for drawing and then watercoloring over when dry, btw.